Concurrent switching of synchronous and asynchronous traffic

ABSTRACT

A network element can be configured for connection to any portion of a communication network: access, transport and core. Moreover, a single network element can be configured to couple subscriber equipment directly to the core portion of the network, thereby permitting the subscriber to bypass the transport portion of the network. Specifically, such a network element can be configured to include a line unit that supports subscriber equipment (also called a “subscriber line unit”), and also to include a line unit to support a link to the core of the communication network (also called a “core line unit”). The subscriber line unit and core line unit are both installed in a single chassis, and each unit can be installed in any of a number of slots in the chassis. Moreover, when configured with appropriate line units, such a network element may support traditional circuit-switched telephony services while simultaneously delivering packet-based voice or data services. The network element provides multi-class service over the entire range of the network because it employs a common switch fabric for handling both synchronous and asynchronous traffic over a common bus.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and incorporates by referenceherein in their entirety the following commonly owned and concurrentlyfiled U.S. patent applications:

[0002] Attorney Docket No. M-8458 US entitled “Optical NetworkRestoration” by Madan Manoharan et al;

[0003] Attorney Docket No. M-8457 US, entitled “Backplane Bus” by JasonDove and Brian Semple;

[0004] Attorney Docket No. M-8645 US entitled “Traffic Merging System”by Jason Dove, Brian Semple, Andre Tanguay, and James Lotz;

[0005] Attorney Docket No. M-9432 US, entitled “Switching of MultipleClasses of Synchronous Data Traffic” by Ying Zhang;

[0006] Attorney Docket No. M-9431 US, entitled “Receive And TransmitPacket Crosspoint” by James Jones;

[0007] Attorney Docket No. M-11554 US, entitled “Automatic ConfigurationOf Equipment For A Network” by James J. Staheli;

[0008] Attorney Docket No. M-11553 US, entitled “Drawing Tool BasedConfigurator” by James J. Staheli; and

[0009] Attorney Docket No. M-11486 US, entitled “Configurator With DualDisplay” by James J. Staheli.

CROSS REFERENCE TO ATTACHMENTS A-I

[0010] The following attachments which describe an illustrativeembodiment of the present invention are a part of the present disclosureand are incorporated by reference herein in their entirety.

[0011] Attachment A entitled “Hardware Architectural Specification;”

[0012] Attachment B entitled “GRX ASIC Functional Specification;”

[0013] Attachment C entitled “GRX ASIC Packet Crosspoint ModuleSpecification;”

[0014] Attachment D entitled “GRX ASIC Synchronous Crosspoint ModuleSpecification;”

[0015] Attachment E entitled “GigaPoint Media Access Controller (GP MAC)Module Specification;”

[0016] Attachment F entitled “GigaPoint Bus Hardware ArchitecturalSpecification;”

[0017] Attachment G entitled “GigaPoint Access Processor (GAP) ASICFunctional Specification;”

[0018] Attachment H entitled “GAP ASIC GigaPoint Adaptation (GA) ModuleSpecification.”

[0019] Attachment I entitled “GAP Virtual Output Queue Controller (VOQC)ASIC Module SpecificationGAP ASIC GigaPoint Adaptation (GA) ModuleSpecification.”

[0020] Attachments A-I contain detailed specifications for variousportions of the network element.

[0021] A portion of the disclosure of this patent document containsmaterial that is subject to copyright protection. The copyright ownerhas no objection to the facsimile reproduction by anyone of the patentdocument or the patent disclosure, as it appear in the U.S. patent andTrademark Office patent files or records, but otherwise reserves allcopyright rights whatsoever.

BACKGROUND

[0022] Traditionally, central office switches that process telephonecalls between subscribers typically use switches called Class 5switches, such as the 5ESS available from Lucent. A telephone instrumentmay be directly connected to such a Class 5 switch as illustrated inFIG. 1 if the telephone instrument is located within 18 kilofoot radius.Beyond the 18 kilofoot radius, support for such telephone instrumentsthat use a copper twisted pair may be provided through a digital loopcarrier (DLC) which has two portions: a central office terminal and aremote terminal. The central office terminal is normally located withinthe central office and communicates with the remote terminal using adigital signal over metallic (such as copper) or optical link (alsocalled “digital line”). The central office terminal of the digital loopcarrier is coupled to the Class 5 switch in the central office and thecoupling may conform to an aggregation interface, such as GR303 (astandard defined by Telcordia). The remote terminal in turn is connectedto a number of telephone instruments. Depending on the hardwareinstalled within the remote terminal, such a remote terminal may alsoprovide a high-speed trunk, such as T1 that may be needed by a businessand/or be coupled via modems to personal computers to support datatraffic.

[0023] The DLC remote terminal may be implemented by a digitalmultiplexer that combines a number of subscriber channels into a singlehigh speed digital signal, and the DLC central office terminalimplemented by a de-multiplexer. Because a digital line cannot carrysignals as far as a corresponding analog line, the digital line oftenrequires a number of digital repeaters to boost signal level. A typicaldigital line of a DLC carries from 24 to 3000 POTS circuits. Note that aDLC central office terminal may be eliminated, e.g. as in case of anIntegrated Digital Loop Carrier System, wherein the digital line isdirectly connected to the Class 5 switch.

[0024] All of above-described equipment up to the Class 5 switch in thecentral office is traditionally referred to as forming the “access”portion of a public switched telephone network (PSTN). The Class 5switch may be associated with a portion of a telephone number, e.g. theportion 252 in a telephone number 408-252-1735. All telephones that areserviced by a single Class 5 switch are normally assigned a telephonenumber that includes a preset prefix, e.g. 252. The Class 5 switchtypically forms connections between telephones within its own servicearea, each of which starts with the preset prefix, e.g. 252. When atelephone instrument within its service area places a call to a numberdifferent from the numbers starting with the preset prefix, the Class 5switch connects the telephone instrument to another switch which may beof a different class, such as a Class IV switch, commonly referred to asa hub switch.

[0025] The hub switch is typically coupled to a number of Class 5switches through a ring of add/drop multiplexers (ADMs). For example,each central office may have a Class 5 switch co-located with andcoupled to an add/drop multiplexer, and in addition the hub switch isalso co-located with and coupled to an add/drop multiplexer. All of theadd/drop multiplexers are connected to one another in a ring topology.Such a ring topology typically contains two optical fiber connectionsbetween each pair of add/drop multiplexers, wherein one of theconnections is redundant, and used primarily in case of failure. Thejust-described ring of add/drop multiplexers that connects a number ofcentral office switches to a hub switch is typically referred to asforming the “interoffice” or “transport” portion of the public telephonenetwork. The hub switch is typically connected to a number of other hubswitches by another portion of the network commonly referred to as“core”.

[0026] To support data traffic, for example, to provide Internet accessto a business, central offices typically contain additional equipmentcalled a DSLAM which provides a digital subscriber line (DSL) connectionto the business. The DSLAM may only service businesses that are within18 kilofeet, e.g. because of the limitations of a copper twisted pairconnection. Such DSLAMs are typically connected inside the centraloffice to an add/drop multiplexer so that data traffic can be routed toan Internet Service Provider (ISP). For businesses located outside of 18kilofeet radius of a central office, a remote terminal of a digital loopcarrier can be used to provide an IDSL service, which is based on theuse of a ISDN link to the central office, via the central officeterminal of the DLC.

[0027] The development of DSLAM, IDC and IDSL applications was theresult of the need for access to the Class 5 switch by remote businessesand subscribers, particularly due to development remote from the Class 5switches. Recently, larger businesses have bypassed this copper remoteaccess to the transport layer of networks using large fiber optic trunkswith large bandwidth capabilities. This new access has been called MetroAccess. Smaller businesses would also benefit from this access, but sofar most applications are too expensive to provide this direct access tosmall enterprise and subscribers. Thus, it would be highly desirable fora network access solution that provides the bandwidth of fiber access inthe place of the typical copper remote access functions, especially thatis cost-competitive with the legacy technology. It would also be highlydesirable if that same solution could be used to performcost-effectively at the remote access level, but through simplesubstitution of line card units to accommodate different types oftraffic, could be deployed to interface with the core itself.

SUMMARY

[0028] In accordance with the invention, a network element can beconfigured for connection to any portion of a communication network:access, transport and core. Moreover, a single network element can beconfigured to couple subscriber equipment directly to the core portionof the network, thereby to bypass the transport portion of the network.Specifically, such a network element can be configured to include a lineunit that supports subscriber equipment (also called “subscriber lineunit”), and also to include a line unit to support a link to core of thecommunication network (also called “core line unit”). The subscriberline unit and core line unit is both installed in a single chassis, andeach unit can be installed in any of a number of slots of the chassis.Moreover, when configured with appropriate line units, such a networkelement may support traditional circuit-switched telephony services,such as DSLAM, DLC and ADM while simultaneously delivering packet-basedvoice or data services.

DETAILED DESCRIPTION

[0029] A network element 11 (FIG. 2) in accordance with the inventionmay be directly coupled to any kind of subscriber equipment (such as atelephone instrument 12, or a modem in a personal computer 13), whenequipped with appropriate line units that support the subscriberequipment. Moreover, such a network element 14 (FIG. 3) may also becoupled (either through a central office terminal of a DLC, or throughanother network element, or even directly) to a switch of any class(such as a central office switch 15 or a hub switch 16), when equippedwith an appropriate line unit. In addition, network element 14 may alsobe coupled directly to a router 17 (FIG. 3), again when equipped with anappropriate line unit. The network element 14 may be further coupled toother network elements 18, 19 and 20 in a ring topology to provideprotection for voice traffic, e.g. support UPSR or BLSR ring functionsdefined by the SONET standard. Network element 14 may also be configuredto protect data traffic as described in U.S. patent application[Attorney Docket No. M-8458] entitled “Optical Network Restoration” byMadan Manoharan et al.

[0030] Also, network elements of the type described herein, whenequipped with the appropriate line units, can be used in the transportportion of the public telephone network and also in the core portion.For example, the network element as described herein may be coupled byan interexchange carrier to network trunk facilities to provideinteroffice call delivery. When used in the core portion, such a networkelement may be provided with line units that are coupled to a longdistance network, and may support dense wave division multiplexing(DVWDM). Therefore, depending on the requirement, a single networkelement 30 (FIG. 5) of the type described herein may be equipped with aline unit 31 (which may also be called “subscriber line unit”)containing circuitry to support subscriber equipment, such as plain oldtelephone service (POTS) on copper twisted pair, and another line unit32 (which may also be called “core line unit”) containing circuitry tosupport the core portion of a communication network, e.g. at OC-48 orOC-192 rates.

[0031] The same network element 30 may also contain another line unit 33(which may also be called “central office line unit”) containingcircuitry to support an aggregation interface (such as GR303 or TR008)to a central office switch (such as the 5ESS available from Lucent),e.g. at DS1 rate. The same network element 30 may also contain yetanother line unit 34 (which may also be called “router line unit”)containing circuitry to support a data interface (such as 1 GigabitEthernet or 10 Gigabit Ethernet).

[0032] Although just four different kinds of line units 31-34 have beendiscussed above, any number of different kinds of line units may be usedin a network element as described herein. For example, oneimplementation supports the following analog, digital, ethernet, andoptical line units: POTS (24 ports), DSL (24 ports), combination of POTSand DSL, DS1 (12 ports), DS3 (8 ports), 10BaseT, 100BaseT, 1GigabitEthernet, 10 Gigabit Ethernet, ESCON (Enterprise Systems Connection),FICON (Fiber Connector), OC3 (4 ports), OC12 (2 ports), OC48 (singleport), Fiber to Business (12° C. 1 ports coming in and one OC12 portgoing out). This implementation also supports a number of differentkinds of these line units, e.g. POTS card may provide just basictelephone service, or provide universal voice grade service, or coinservice, or transmission only service (2 wire or 4 wire), or privateline automatic ring-down service (PLAR), foreign exchange service.Furthermore, the network element may be configured with one or morecards that interface with a Class 5 switch or with a router: e.g. DS1card with GR 303 aggregation, or PLAR, or transmission only, or OC3(packet), or OC12 (packet), or OC48 (packet).

[0033] Each line unit 31-34 described above is coupled by one or morebuses 41-44 (FIG. 5) to the switch unit 35, physically located in ahigh-speed area of a backplane of chassis 39. Depending on theembodiment, the one or more buses 41-44 may be of any kind, synchronousor asynchronous, and may be either parallel or serial. Such busesoperated at 3.1 Gbps. Information is transmitted over such buses of thebackplane in discrete units called “frames,” and a number of frames aregrouped into a superframe, e.g. in a manner similar to SONET. Theinformation on such buses may be generated by circuitry (labeled GAP inFIG. 5), in each line unit (labeled LU in FIG. 5), in a format describedin, U.S. patent application [Attorney Docket No. M-8457] entitled“BACKPLANE BUS” by Jason Dove and Brian Semple. In one example, suchframes are grouped into a 6 millisecond superframe. The physical layerfor the backplane buses is described in IEEE 802.3 z. Such buses may becoupled via a connector, e.g. a 5-row by 10 VHDM connector in each LUslot of chassis 39, and and an 8-row by 60 VHDM connector in the RAPslots.

[0034] In addition to containing line units (which can be of differentkinds or all of the same kind), the above-described network element 30also contains a cross-connect to transfer traffic among various lineunits. For example, traffic to and from subscriber equipment (alsocalled “subscriber traffic”), such as a telephone instrument or aprivate branch exchange (PBX), that is carried by a subscriber line unit31 is switched by such a cross-connect to core line unit 32. Therefore,core line unit 32 carries the subscriber traffic sequentially, therebyto pass the subscriber traffic to and from the core of the communicationnetwork, e.g. to support a long distance telephone call. The transfer oftraffic between line units and the cross-connect changes with time, sothat at a different moment in time, traffic to/from subscriber line unit31 may be switched by such a cross-connect to/from router line unit 34,e.g. if the traffic originates from and has as its destination a modem(which modem may be coupled to a different port of line unit 32 from theport to which the above-described telephone instrument is coupled).

[0035] A network element of the type described above implements in itsline units a number of functions that were performed by a number ofdiscrete products in the prior art. Therefore, a network element of thetype described herein eliminates the need for a communication serviceprovider to deploy such discrete products. Specifically, one embodimentof the network element eliminates the need for digital loop carriers(DLCs), DSLAMs, add/drop multiplexers (of both types: access andtransport). Instead, a communication service provider can simply use asingle chassis of the network element, and install whichever subscriberline unit is needed to support the type of services required by itscustomers. If necessary, such a single chassis may also be configured tocontain a core line unit to connect to the core network. Also, ifnecessary, the number of chassis in a single network element may beincrementally increased (e.g. up to a total of 5 chassis which fit in asingle cabinet). Therefore, a network element of the type describedherein can be used to provide services at the network edge, e.g. tosmall businesses and at the same time to connect Class 5 switches tolong-distance trunk facilities, and/or interexchange transportfacilities. Therefore, a network element of the type described hereinmay be used in any portion of the entire communication network, toprovide any service.

[0036] In one embodiment, each of line units 31-34 (FIG. 5) areinstalled in a chassis 39 in which is also installed a unit 35 (whichmay also be called “switch unit”) that contains the above-describedcross-connect. Each of units 31-35 may be implemented in a modularmanner, e.g. as cards that can be inserted into and removed from chassis39. There may be one or more additional cards that act as standby incase of a failure of a portion of the circuitry in such cards. However,in other implementations, it is not necessary for the units to bemodular, or to be implemented in cards. For example, switch unit 35 maybe built into a chassis in an alternative implementation. In onespecific implementation, switch unit 35 and a line unit are implementedin a single card, such as a common control card discussed in AttachmentA in reference to RAP. The line unit that is installed on the RAP cardmay contain circuitry that supports any traffic rate, such as OC3, OC12and OC48.

[0037] In one implementation, chassis 39 is 19 inches wide and contains23 slots, whereas in another implementation chassis 39 is 23 incheswide, and provides 29 slots. Width W (FIG. 5) is selected so as to allowchassis 39 to be installed in a rack commonly found in a central office.Regardless of the number of slots present, in one embodiment one slot inthe center is reserved for a card that contains an interface unit (tointerface with humans), and two slots on either side of the center slotare resered for two copies of the above-described common control card,wherein one copy is used as a standby for the other copy. The usage ofslots in one embodiment is described in the following table: SLOT 1through SLOT 10 Line Units (incl. transport) SLOT 11 Common Control(RAP) SLOT 12 Interface Unit (AMP) SLOT 13 Common Control (RAP) SLOT 14through SLOT 23 Line Units (incl. Transport)

[0038] Switching of the two kinds of traffic (voice and data) asdescribed above, by the cross-connect in switch unit 35 is performed intwo separate circuits, namely a synchronous cross-connect, and anasynchronous cross-connect that are respectively described in the U.S.patent applications, Attorney Docket No. M-9432 US, entitled “Method andApparatus for Efficient Switching of Multiple Classes of SynchronousData Traffic” by Ying Zhang and Attorney Docket No. M-9431 US, entitled“Gigapoint Receive And Transmit Packet Crosspoint” by James Jones, bothof which were incorporated by reference above. The synchronouscross-connect, and the asynchronous cross-connect operatesimultaneously, i.e. one cross-connect switches traffic to/from one setof input-output ports while at the same time the other cross-connectswitches traffic to/from another set of input-output ports. Thejust-described input-output ports are of the cross-connect as a whole,and their division into the two sets changes with time, as describedbriefly herein and in detail in Attachments A-I.

[0039] A network element of the type described above may be used togroom a broad range of traffic classes, including ATM, Frame Relay, IP,STS and TDM traffic. In one embodiment, any combination of the foregoingtraffic types can be switched between a core network and/or PSTN andbusiness users and/or residential users. A communication network of thisembodiment includes two network elements that are hereinafter referredto as a Host Node (HN) that typically resides at a central office (CO)and a Flex Node (FN) that resides at a remote terminal to whichindividual users have access. Although in this particular embodiment (asdescribed in detail next) the network elements are used as Host Nodesand Flex Nodes in other embodiments such network elements may be used asother components of a communication network, such as add-dropmultiplexers.

[0040] Host Node 110 and Flex Node 112 (see FIG. 6) of this embodimentcontain many of the same components, e.g. each node has at least a firstshelf 114 a, 116 a, respectively. Shelves 114 a, 116 a of have a numberof slots for receiving and coupling circuit boards (118, 120respectively) to a common back-plane (not shown) by which the circuitboards of each shelf communicate with one another. Shelf 114 a of HN 10has two slots for receiving an active and a redundant Routing andArbitration Processor board (RAP(A) 124 a and RAP(B) 124 brespectively). Shelf 116 a of FN 112 has two slots for receiving anactive and redundant Routing and Arbitration Processor board (RAP(A) 122a and RAP(B) 122 b respectively). The RAP (for both nodes 110, 112)performs the primary functions providing an interface for up to 32full-duplex data ports over which data traffic is received ortransmitted, routing the data traffic between the ports, and tocondition the data traffic for routing. Typically, only one of the RAPboards is active, while the other remains idle unless pressed intoaction as a result of a failure of the first RAP board. Each shelf 114 aand 116 a of nodes HN 110 and FN 112 also has one slot for anadministration and maintenance processor board (AMP) 115. The AMPprovides test access, alarm status, application hosting, and the AMP 115provides an Ethernet connection, for Network Element Management.

[0041] Shelves 114 a and 116 a of nodes 110, 112 also have at leasttwenty slots to receive circuit boards that form line units 118, 120respectively. As noted above, such line units may be implemented ascircuit boards that are specifically designed to transmit and receiveparticular forms of traffic. For example, some line units have ports andcircuitry to interface with POTS terminals. The same line units may haveother ports designed to interface with DS-1, DS-3, DSL, STS or opticalstandards such as OC-3, OC-12 and OC-48 for example. Moreover, all portsof certain line units may be of the same kind, e.g. a single line unitmay have only POTS ports.

[0042] All of the line units 118, 120 of a given shelf 114 a, 116 aprovide communication between some number of ports to the outside world,and one or more backplane buses of the type described above. In oneimplementation, the backplane buses are full duplex serial buses (in onespecific example illustrated in the Attachments A-Z such buses arecalled Gigapoint buses) coupled to the active RAP(A) and inactive RAP(B)of the shelf through the backplane (not shown). In one embodiment, eachslot of a given shelf has four such serial buses by which each line unitplugged therein is coupled to the RAP(A) of that shelf and four suchserial buses by which the line unit plugged therein is coupled to theRAP(B) of that shelf.

[0043] In a typical embodiment of the system of FIG. 6, a circuit boardslot of shelf 1114 aof HN 110 is used for a two port OC-12 circuit board118(A), 118(B) that provides dual SONET OC-12 interfaces 113 a, 113 bwhen RAP(A) 124 a is active, and standby interfaces 113 c, 113 d ifRAP(B) becomes active in the event RAP(A) 124 a fails. The SONETinterfaces 113 a-d can be used to provide connectivity to an Edge/CoreNetwork 111. The line unit 118(A)(B) is coupled through the backplane toRAP(A) 124 a through two active serial buses (and to RAP(B) 124 b aswell through one inactive bus for back-up) operating at 3.11 Gbps. Oneembodiment of line unit 118 can provide STS, ATM and or PPP transportmodes. An enhancement to allow the transport of both (point-to-pointprotocol (PPP) and ATM can be provided via the Pre-emptive ATM over PPPmethod. In this application the HN 110 is used as either a transport oraccess multiplexer. Line unit 118 can also be used for communicationbetween the HN 110 and FN 112.

[0044]FIG. 6 illustrates that another slot of shelf 114 a of HN 110 isused for a line unit 119(A), 119(B) that provides for communicationbetween HN 110 and RAP(A) 122 a (or RAP(B) 122 b) of FN 112. Oneembodiment of line unit 19(A)(B) can have up to four OC-3 ports, therebyproviding multiple SONET OC-3 interfaces that can be used to communicatebetween the HN 110 and FN 112 nodes. In this application the HN 110 istypically used as an access multiplexer. Fiber egress to line unit 119is via four SC connectors. One embodiment of line unit 119 provides STS,ATM and or PPP transport modes. An enhancement to allow the transport ofboth PPP and ATM can be provided via the Pre-emptive ATM over PPPmethod.

[0045] The circuit board slots of shelves 114 a, 116 a of nodes 110, 112can be populated with optical line units as described above or withadditional embodiments of line units 118, 120 that provide standardinterfaces to several typical forms of data and/or voice traffic sourcedby business and residential users. For example, another embodiment of aline unit 120 is a POTS circuit board that supports up to 25 POTSinterfaces. The POTS interfaces support both loop and ground start aswell as provisionable characteristic loop impedance and return loss. Thebandwidth requirements for this board are low and thus only one activeand one standby full duplex serial bus running at 3.11 Gbps are requiredto couple this line unit to the RAP(A) 122 a and RAP(B) 122 brespectively.

[0046] Another Line Unit that can be used in the system is a 24 portAsymmetric Digital Subscriber Line (ADSL) board that supports 24 FullRate ADSL interfaces. ADSL is a modem technology that converts existingtwisted-pair telephone lines into access paths for multimedia andhigh-speed data communications. ADSL can transmit up to 6 Mbps to asubscriber, and as much as 832 Kbps or more in both directions (fullduplex). The line coding technique used is discrete multi-tone (DMT) andmay also function in a G.Lite mode to conserve power. The circuit boarddoes not include POTS splitters, which must be deployed in a sub-systemoutside of the shelf 116 a. One embodiment of the 24 port ADSL line unitis constructed with quad port framers. Because the bandwidthrequirements for this line unit are typically low, once again only oneactive and one standby bus running at 3.1 Gbps are required to couplethe line unit to the RAP(A) 122 aand RAP(B) 122 b of shelf 116 a.

[0047] Another line unit that can be employed with the system of FIG. 6is a twelve port POTS/DSL combo-board that supports12 POTS and 12 FullRate ADSL interfaces. The combo-board is the melding of half of a POTSand half of an ADSL line unit as discussed above. The POTS interfacessupport both loop and ground start as well as provision ablecharacteristic loop impedance and return loss. The ADSL line-codingtechnique used is DMT and may also function in a G.Lite mode to conservepower. In one embodiment, quad port ADSL framers may be employed tocondition the ADSL traffic. Because the bandwidth requirements for thisline unit are typically low, only one active and one standby serial busrunning at 31. Gbps are required to interface the line unit with theRAP(A) 122 a and RAP(B) 122 b respectively.

[0048] Another line unit that can be employed within the systemillustrated in FIG. 6 is a twelve port DS-1 board that supports up to 12DS-1 interfaces. An embodiment of the DS-1 line unit supports DSX-1interfaces. Optionally, the card supports twelve dry T-1 interfaces.Switching current sources are included to support twelve powered T-1interfaces. Again, because the bandwidth requirements for this line unitare low, only one active and one standby bus running at 3.1 Gbps arerequired to connect the line unit to the RAP(A) and RAP(B) respectively.For this line unit, data traffic flows over a Utopia 2 interface.Control and provisioning information is communicated over a PCI bus.Control and provisioning information for T1 framers/line interfaces iscommunicated over a serial interface. An edge stream processor (ESP)provides an ATM adaptation layer (AAL) 1/2 adaptation function for all12 framer interfaces. The ESP terminates structured DSO traffic TDMcross-connect switching or time stamps asynchronous DS1 traffic forHi-Cap transport. The ESP processor is also capable of terminating PPPframed DS1 traffic for either Layer 2 tunneling (L2TP) or Layer 3routing.

[0049] Another line unit 118, 120 that can be used in the system of FIG.6 is an eight port DS3 board that supports up to 8 DS-3 interfaces. Inone embodiment of this line unit, each interface may be provisioned toterminate either an ATM UNI (ATM unicast), PPP or ChannelizedHi-Capacity DS3 service. A routing stream processor supports either ATMor PPP by queuing and scheduling DS-3 traffic for packet transportthrough the RAP. A DS3_Mapper supports the Hi-Cap DS3 by mapping DS-3traffic into an STS1 channel for low latency transport through the RAP.

[0050] Another line unit 118, 120 that can be used in conjunction withthe system of FIG. 6 is a single port STS1 board. In one embodiment ofthe STS-1 board, a mode selectable single STS 1 or DS-3 interface issupported.

[0051] Another line unit 118, 120 that can be used in conjunction withthe system of FIG. 6 is a single port OC48 Interface board. The singleport OC48 line unit provides a single SONET OC-48 interface to provideconnectivity to the Edge/Core Network. In this application the HN 110 isused primarily as a transport level add/drop multiplexer. In a preferredembodiment, fiber egress is via two SC connectors. SONET framers provideSTS, ATM and or PPP transport modes. An enhancement to allow thetransport of both PPP and ATM is provided via a Pre-emptive ATM over PPPmethod.

[0052] Still one more line unit 118, 120 that can be used in conjunctionwith the system shown in FIG. 6 is a twelve port Fiber to the Business(FTTB) board. The twelve port FTTB assembly provides a single OC-12SONET interface out and twelve OC-1 SONET interfaces in. In oneembodiment of this line unit, a unique integrated splitter arrangementallows sharing of the single laser diode over twelve businesssubscribers. Twelve discrete PIN diode receivers will be provided toallow a single interface per each of the twelve business subscribers.This method allows simple and inexpensive fault isolation and efficientbandwidth management amongst the entire pool of business subscribers.The interface provided to the subscriber is a single fiber with a singlelambda down and a separate lambda up. This arrangement reduces fiberbulk and cost. The dual Lambda arrangement allows a simpler splitterimplementation to be realized in a “silica on silicon” waveguide device.The FTTB line unit is coupled through the backplane to RAP(A) 124 athrough one active serial bus (and to RAP(B) 124 b as well through oneinactive bus for back-up) operating at 3.11 Gbps.

[0053] Thus, it can be seen from the foregoing discussion that thenetwork element is designed to permit the largest number of customerapplications to be supported within a single shelf HN and single shelfFN. While the system of FIG. 6 is optimized towards a single shelf pernode configuration, expansion to a multi-shelf per node configuration isalso supported in a deterministic and modular fashion. Typicallyco-located shelves are connected in a Uni-directional Path Switched Ring(UPSR) arrangement via the RAP mounted optics as illustrated in FIG. 6by the addition of shelves 114 b, and 114 c to HN 110. This provides asimple, incremental means of local expansion. Local expansion can alsobe implemented in a point-to-point fashion, however, at the expense ofslots and cost. A single HN 110 may host many FNs 112 in a variety oftopologies. FNs 110 may be subtended from an HN 110 in point-to-point,linear chain, branch and continue, UPSR or bi-directional line switchedring (BLSR) arrangement. An extremely large network of over 20,000subscribers may be constructed from the HN/FN hierarchy as illustratedin FIG. 6.

[0054] Line units 118, 120 (FIG. 6) are split out into an input side 130a and output side 130 b for clarity in FIG. 7 (which is also shownwithout the AMP). Those of skill in the art will recognize that theinput and output paths of each line unit 134 a(1-n), 134 b(1-n)respectively, will typically reside on one circuit board and may evenshare some of the same circuits. Each output path 134 b(1-n) produces anoutput 136 b(1-n) in the form of cells, samples and packets. The linecards can be of a lower bandwidth nature (e.g. line unit 138 a 1/38 b1), such as the twenty-four port POTS unit, the twenty-four port DSLunit, and the twelve port POTS/DSL combo unit as previously described.Some of the line units are high bandwidth (e.g. line unit 134 an/134bn), such as the twelve port DS1/T1 unit, the eight port DS3 unit, andthe ST-1, OC-3, OC-12 and OC-48 units, all of which require an ESP/RSP142 a, 142 b to perform pre-processing of the traffic.

[0055] Line unit input paths 134 a(1-n) perform the function ofinterfacing with the physical layer of a data source to receive datatraffic over inputs 136 a(1-n) in the form of cells, samples or packets,depending upon the source type, and then grooming the traffic throughits circuitry (called GAP which is an abbreviation for GigaPoint AccessProcessor) 140 a(1-n) so that it can be switched by the matrix 137 ofswitch 133 to any one or more of the line unit output paths 134 b(1-n).The line unit output paths 134 b(1-n) perform the function of taking therouted traffic and converting it back to the physical layer formatexpected by the receiver to which it is coupled. The interfacingfunction is represented by input path circuits Phy 138 a(1-n) and Phyoutput path circuits 138 b(1-n). The traffic for higher bandwidthtraffic sources often requires an additional layer of circuitry 142 a,142 b for grooming the data traffic, such as an RSP, an ESP and/or quadframers.

[0056] The input path GAP 140 a(1-n) for each line unit input path 134a(1-n) transmits groomed and serialized data traffic over one or morehigh-speed serial input buses 132 a(1-n) to the switch 133, where theserialized data is converted to parallel data for switching. Withrespect to the output path 134 b(1-n) of each line unit, a transmitportion of output path GAP 140 b(1-n) residing within switch 133 (notshown) serializes switched data traffic and transmits it over high-speedserial output buses 132 b(1-n) to the receive portion of each GAPresiding in the line unit output paths. From there, the data traffic isadapted back to the physical layer protocol spoken by the destinationfor the outgoing traffic. The input path GAP 140 a(1-n) of each lineunit provides data to switch 133 as asynchronous packet traffic, TDM andmulticast synchronous packet traffic, and channelized STS data traffic.Likewise, the output path GAP 40 b(1-n) of each line unit receives datain one of the foregoing forms from the switch 133, and adapts it to therequisite physical layer of the traffic destination.

[0057] The switch 133 includes the active RAP(A) 144 and back-up RAP(B)146. Each RAP includes a switch unit (called GRX which is anabbreviation for GigaPoint Routing Cross-connect) 139. GRX 139 furtherincludes an arbiter 135 and a matrix 137 by which the conditioned datatraffic arriving over the input side of any of the serial buses isswitched to the appropriate output side of one or more of the serialbuses coupled to the destination for that conditioned traffic.

[0058] In one embodiment (FIG. 8), there are twenty-four I/O ports forGRX 139 that are coupled to the backplane. Twenty of the I/O portscouple line units 134(1-n) to the GRX 139 through full-duplex serialbuses 132(1-20). One port 132(21) couples RAP(A) 44 to the outside worldthrough input 136(21). Another port that is not shown couples RAP(B)(also not shown) to the outside world and the last port (not shown)couples the AMP (not shown) of shelf 116 a to the outside world. Theline units 134(1-n) are shown with both their input and output paths.

[0059] One possible combination of specific line units is illustrated inFIG. 8 to illustrate the versatility of the system. Twenty-four portPOTS unit 134(1) interfaces to the GRX 139 over serial bus GP_(—)1132(1), and has twenty-five telephone interface inputs 136(1) coupled tofive quad codecs 138(1), which in turn interface with GAP 40(1). Atwelve port DS1 unit 134(10) having twelve DS1 interfaces coupled tothree quad Ti framers 138(10), the outputs of which are processed by ESP142(10), sends and receives conditioned traffic through GAP 140(10) toGRX 139 over serial bus GP_(—)10 132(10). Four port OC3 units 134(11)and 134(n) are each coupled to GRX 139 over two serial buses GP_(—)11132(11), GP_(—)12 132(12) and GP_(—)19 312(10), GP20 132(20)respectively. Each unit provides a total bandwidth equivalent to OC-12,handling bidirectional OC-3 traffic over OC-3 I/Os 136(11) and 136(n)respectively. The line units 134(11), 134(n) interface with the OC-3traffic by way of OC-12 framer/phy 138(11), 138(n) respectively and datais transferred to and from the GRX 139 by way of GAP 40(11), 40(n)respectively.

[0060] Those of skill in the art will recognize that any combination ofthe line units described herein, or any that are designed to interfacewith and condition data traffic to be transmitted and received over abackplane bus by way of a GAP in the form of asynchronous packettraffic, TDM and multicast synchronous packet traffic, and channelizedSTS data traffic can be employed in shelf 116 a of FIG. 8.

[0061] The present invention is able to serve a broad range of networkaccess functions because it handles both synchronous and asynchronousclasses of traffic over a common fabric. In prior art multi-classsolutions, these types of traffic are typically handled separately overseparate bus systems. Such a solution to the problem is not desirablebecause though it makes handling the traffic simpler, it does notprovide advantages of flexibility and lower cost.

[0062] With reference to FIG. 9, a conceptual block diagram of thepresent invention is depicted that facilitates seeing the flow of thedifferent types of traffic through the common switch fabric. Line unit118, 120 consists of GAP 134 a,b (both transmit and receive paths). Aspreviously discussed, The GAP 140 interconnects traffic from the serial(GigaPoint) bus 132 a,b (transmit and receive) to physical interfacesthat make up part of the line units such as OC-48, POTS etc. The GAP 140receives and transmits TDM and packet base traffic over the GigaPointBus 132. The Gap 140 also transmits local queue status over theGigaPoint bus 132. It receives control and arbitration information overthe GigaPoint Bus 132, and maps POTS Codec traffic into an internalpacket format. The GAP supports VoQ with 2 classes of service toward theGigaPoint bus. The GAP supports AAL-5 by way of a Hardware SAR(Segmentation and Reassembly) engine, termination of SONET transportoverhead bytes and implements a time slot interchange (TSI) for DSOtraffic. For more information regarding the GAP, refer to the “GigaPointAccess Processor (GAP) ASIC Functional Specification,” attached heretoas Attachment G.

[0063] The GAP includes a Transmit/Receive GP MAC (Media AccessController), that handles transmitting and receiving communicating bothSTS and packet traffic through the serial high speed GigaPoint busthrough SerDes (Gigabit Ethernet serializer/deserializer) 152. Themixture of packet and STS traffic is simply squeezed down andtransmitted over a high speed link to transport the traffic between theGAP, across the backplane of the system, and the common switch fabricrepresented by GRX 139. Another transmit/receive SerDes 154 resides onthe GRX 139 that is interfaced with another receive/transmit MAC 156.For information regarding the details regarding the high-speed busarchitecture, refer to the “GigaPoint Bus Hardware ArchitecturalSpecification,” which is attached hereto as Attachment F.

[0064] In the GRX139, the receive GP MAC 156 a accepts combinedasynchronous and synchronous traffic from a line unit through the SerDescore and distributes it to the packet crosspoint 158 and synchronouscrosspoint 160 respectively. STS bytes and synchronous packets (TDM andmulticast) are driven to the synchronous crosspoint 160 over a 40-bitparallel bus. Unicast packets are sent over a 64-bit FIFO interface tothe packet crosspoint 158. An eight-bit packet arrival word is extractedby each receive MAC and driven to the arbiter 135. The arrival word issent with an arrival strobe, as well as downstream GigaPoint and grantbackpressure signals.

[0065] The GRX transmit GigaPoint MAC 156 b receives data bound for theserial bus to line unit 188, 120 over three buses; the 64-bitasynchronous packet bus 164, the 40-bit synchronous bus 166 and the8-bit arbiter bus 162. Asynchronous bus data is read from the packetcrosspoint's output FIFO. Synchronous data (STS, TDM and multicastpackets) is received from the synchronous crosspoint at timeslotsrelative to superframe sync and in accordance with bandwidth allocationof the particular link by way of a channel map configuration. Packetgrant information is transported from the GigaPoint arbiter 135 to theTX MAC in a manner similar to that of packet arrival information.

[0066] For more information regarding the implementation of the GP MAC,refer to the “GigaPoint Media Access Controller (GP MAC) ModuleSpecification” attached hereto as Attachment E.

[0067] A block diagram of the GRX ASIC is depicted in FIG. 10. In thereceive path, the GigaPoint Rx MAC modules 156 a(1)-a(n) interface withthe GigaPoint SerDes receiver 154(1). The Rx MACs extract packet arrivaland backpressure fields from the GigaPoint packet headers and pass theinformation to the GigaPoint Arbiter 135 and GigaPoint Tx MACs 156a(1)-a(n) respectively. The GigaPoint Rx MAC modules also provide datalayer decoding by splitting STS, TDM, multicast packet, and unicastpacket traffic. In one embodiment, only unicast packet traffic is routedto the Packet Crosspoint 158 and the other traffic types are routed tothe Synchronous Crosspoint 160. Loosely scheduled TDM and multicasttraffic could be routed through the packet cross-connect 158, but it isactually more convenient to route these types of packet traffic throughthe synchronous cross-connect 160 as well. In the transmit path, theGigaPoint Tx MAC 156 b(1)-b(n) modules combine the various traffic typesoutput by the crosspoints 158, 160 and output them to the GigaPointSerDes Transmitters 154(1)-n. Also, the Tx MACs insert packet grants andbackpressure fields into the GigaPoint packet headers. The PacketCrosspoint 158 snoops on the Packet Grant 302 and Packet Arrival 300interfaces in support of the grant audit mechanism.

[0068] For detailed information concerning the implementation detailsfor the synchronous cross-connect 160, refer to cross-referenced U.S.application entitled “Switching of Multiple Classes of Synchronous DataTraffic,” by Ying Zheng and the “GRX ASIC Synchronous Crosspoint ModuleSpecification,” attached hereto as Attachment D. For more detailedinformation regarding the asynchronous cross-connect 158, refer tocross-referenced U.S. application entitled “Receive And Transmit PacketCrosspoint” by James W. Jones and the “GRX ASIC Packet Crosspoint ModuleSpecification,” attached hereto as Attachment C.

[0069] In one embodiment, traffic carried over the serial links betweenthe GAP 140 and the GRX 139 is classified in to three primary groups. Asshown in FIG. 11, 60 GigaPoint channels 310 are pre-allocated for STS312, TDM/Multicast 316, or Unicast traffic314. Fixed TDM FLP (fixedlength packet) slots are then defined within the channels allocated toTDM. Each TDM FLP slot is 64 bytes long and remains at a fixed locationwith respect to the 125 us frame sync until the TDM pipe is re-sized.TDM traffic shares its bandwidth with Multicast traffic, which meansthat software needs to take into account the bandwidth requirements ofMulticast when provisioning TDM.

[0070] Each GigaPoint bus can support the transport of STS traffic indesignated timeslots in a 125 us frame window. Traffic in channelssharing the same channel designator can be merged as it is passedthrough the 24:1 masked muxes. This function allows a VT1.5cross-connect function to be implemented by aligning VT1.5s within theappropriate STS channel(s).

[0071] Thus, those of skill in the art will recognize that combining androuting both asynchronous and synchronous traffic across a common fabricreduces system implementation size as well as makes the invention easilyconfigured to handle numerous legacy applications network applications,as well as to combine such applications into one system. Moreover, theflexibility in provisioning bandwidth among the traffic types makes theinvention configurable for serving applications from the subscriber edgeof a network up to the edge of the core of a network.

[0072] Numerous modifications and adaptations of the embodimentsdescribed herein will be apparent to the skilled artisan in view of thedisclosure.

[0073] While in one embodiment, a network element of the type describedherein does not provide call processing functions, in another embodimentcall processing may be supported by a network element of the typedescribed herein.

[0074] Numerous such modifications and adaptations are encompassed bythe attached claims.

1. A network element for a communication network, the network elementcomprising: a first line unit comprising circuitry to support subscriberequipment; and a second line unit comprising circuitry to support a linkto core of the communication network; and a chassis, each of the firstline unit and the second line unit being installed said chassis.
 2. Thenetwork element of claim 1 further comprising: a switch unit having afirst port coupled to the first line unit and a second port coupled tothe second line unit, the switch unit being installed in said chassis.3. The network element of claim 1 wherein: the first line unit carriestraffic from and to the subscriber equipment; and the second line unitcarries said traffic sequentially thereby to pass said traffic to andfrom said core of the communication network.
 4. The network element ofclaim 1 further comprising: a switch unit having a first port coupled tothe first line unit and a second port coupled to the second line unit,the switch unit being installed in said chassis, the switch unitcomprising a cross-connect.
 5. The network element of claim 4 wherein:the cross-connect includes a synchronous cross-connect and anasynchronous cross-connect.
 6. The network element of claim 5 wherein:at one time the synchronous cross-connect transfers traffic between thefirst line unit and the second line unit; and at another time theasynchronous cross-connect transfers traffic between the first line unitand the second line unit.